#include<stdio.h>

void inspos(char *s1,char *s2,int pos){
    int len=0;
   while(*(s1+len)!='\0'){
        len++;
    }
    for(int i=len;i>=pos;i--){
        s1[i+2]=s1[i];
    }
    s1[pos]=s2[0];
    s1[pos+1]=s2[1];
}

int main(){
    char s1[64] = {"hello world"};
    char s2[3] = {"ni"};
    int pos = 3;
    inspos(s1,s2,pos);
    printf("%s",s1);
    

    return 0;
}